Transcript Slide 1
Strategies for detection of melamine in milk products Xin Wu Literature Seminar 05/03/2010 Objective Compare two methods to detect of melamine in milk products. Melamine 2,4,6-triamino-s-triazine, MM In manufacture of: Plastics, Flame retardant Fertilizer Toxicity Acute toxicity Chronic toxicity Contaminants in many kinds of food http://www.toothpastefordinner.co m/archives/2008/Dec/ Summary of the detection methods Nitrogen methods Kjeldahl method Most traditional subtractive method veracity is poor Other methods sublimation and picric acid weight methods high veracity, complicated operation, time-consuming GC with UV/MS detection Expensive, derivatization before GC .sensitive LC-MS/MS LOD low, sensitive but complicated Kjeldahl method Degradation: Protein + H2SO4 → (NH4)2SO4(aq) + CO2(g) + SO2(g) + H2O(g) Liberation of ammonia: (NH4)2SO4(aq) + 2NaOH → Na2SO4(aq) + 2H2O(l) + 2NH3(g) Capture of ammonia: B(OH)3 + H2O + NH3 → NH4+ + B(OH)4– Back-titration: B(OH)3 + H2O + Na2CO3 → NaHCO3(aq) + NaB(OH)4(aq) + CO2(g) + H2O Paper I Residue analysis of melamine in milk Products by micellar electrokinetic capillary chromatography with amperometric detection Jinyan Wang, Lianmei Jiang, Qingcui Chu , Jiannong Ye Food Chemistry 121 (2010) 215–219 Capillary electrophoresis (CE) Separate ionic species by their charge and mass. UV or fluorescence detection Advantages of CE over HPLC Micellar electrokinetic chromatography Modification of capillary electrophoresis Sample separated between micelles and buffer C(Surfactant) >CMC in open capillaries under alkaline conditions Sodium dodecyl sulfate (SDS) Shegeru,Japan Chemical Journal 8:291-301 Materials and Preparation laboratory-built CE–AD system MM ; Milk and infant formula milk powder samples; running buffer (8 mmol/L SDS/20 mmol/L H3BO3– Na2B4O7 solution) Weighed-Extracted by ultrasonic bath-filtered-CEAD system Effect of the potential applied to the working electrode 1 Above 750 mV, oxidation current increased rapidly with applied potential. 2 Above 1200 mV, unstable baseline 3 1150mV is best choice Effects of the pH value 1 pH range 7.4-9.2 2 MM always overlapped with the unknown compound peak in real samples 3 pH is optimum pH Effects of SDS 1 at a fixed pH value 7.4 2 longer retention time with increased concentration of SDS 3 8 mmol/L SDS is optimum concentratioin Electropherograms Recovery of samples Conclusion A new method of MECC-AD to residue analysis of melamine For the real world sample Run time is 9 min Good recoveries ranging from 83.3% to 105.5% of MM were determined Practical method with sample preconcentration Paper II A sensitive and validated method for determination of melamine residue in liquid milk by reversed phase high-performance liquid Chromatography with solid-phase extraction Hanwen Sun, Lixin Wang, Lianfeng Ai, Shuxuan Liang, Hong Wu Food Control 21 (2010) 686–691 HPLC separate, identify, and quantify compounds based on their idiosyncratic polarities and interactions with the column's stationary phase A pump propel the mobile phase and analyte through densely packed column Widely used Various types of HPLC http://en.wikipedia.org/wiki/File:Hplc.JPG solid-phase extraction (SPE) Concentrate and purify samples for analysis Used to separate analytes from a variety of matrices: (1) blood (2) animal tissue (3) water etc. Mobile phase (liquid and analyte); Stationary Phase (solid) Silica Materials and Methods Cleanert PCX-SPE cartridges (3 mL/60 mg), LC–MS/MS (Thermo Electron Corp., San Jose, CA, USA), an SeQuant ZIC HILIC column. Sodium n-heptanesulfonate, acetonitrile, melamine, 1% trichloroacetic acid, 2.2% lead acetate solution, liquid milk sample Confirmation by LC-MS/MS, Sample extraction and clean- up, HPLC analysis, The effects of pH pH =2.7 is the optimum value The effects of the ratio (v/v) between 10 mM sodium n-heptanesulfate (pH 2.7) and acetonitrile retention time of melamine shorted with the decrease of ratio value. The LOD and recovery of sample Conclusion A new method of RP-HPLC-SPE to residue analysis of melamine Real world sample Run time is 10 min Good recoveries ranging from 85.5–99.3%of MM were determined Comparison of the two methods TIME(min) LOD (10-6g/ml) Recovery MECC-AD 9 2.1 83.3% to 105.5% RP-HPLC-SPE 10 3 85.5–99.3% Acknowledgements Professor Kermit K. Murray Murray Research Group Audience Any questions?